<h1>Runtime Profiler API</h1>

	<p>The profiler API can be used by dynamically loaded profiler
	modules to monitor different aspects of a running program. The
	API is also usable by embedders without having to compile a
	profiler module.

<h2>Profiler Modules</h2>

	<p>A profiler module is simply a shared library with a single
	exported function which is the entry point that Mono calls at
	startup. It must have the following signature:

	<pre><code class="mapi-codeblock">
void mono_profiler_startup_example (const char *desc)
	</code></pre>

	<p>Here, the <code>example</code> portion of the function name is
	the name of the profiler module. It must match the shared library
	name (i.e. <code>libmono-profiler-example.so</code>). <i>desc</i>
	is the set of arguments that were passed from the command line.

	<p>For example, a bare bones profiler module might look like this
	(<code>example.c</code>):

	<pre><code class="mapi-codeblock">
#include &lt;mono/metadata/profiler.h&gt;
#include &lt;stdio.h&gt;

struct _MonoProfiler {
	int dummy;
}

static MonoProfiler profiler;

static void
runtime_inited (MonoProfiler *prof)
{
	printf ("Hello World");
}

void
mono_profiler_init_example (const char *desc)
{
	MonoProfilerHandle handle = mono_profiler_create (&amp;profiler);
	mono_profiler_set_runtime_initialized_callback (handle, runtime_inited);
}
	</code></pre>

	<p>To compile this module, a C compiler must be invoked in a
	similar fashion to this, on Linux:

	<pre><code class="mapi-codeblock">
gcc -fPIC -shared -o libmono-profiler-example.so example.c `pkg-config --cflags mono-2`
	</code></pre>

	<p>Or on OS X:

	<pre><code class="mapi-codeblock">
gcc -undefined suppress -flat_namespace -o libmono-profiler-example.so example.c `pkg-config --cflags mono-2`
	</code></pre>

	<p>You can then load the module using:

	<pre><code class="mapi-codeblock">
mono --profile=example hello.exe
	</code></pre>

	<p>(Note that adjusting <code>LD_LIBRARY_PATH</code> may be
	necessary in order for the dynamic linker to find the module.)

<h2>Profiler Functions</h2>

	<p>These are the functions usable for profiling programs.

	<p>Each function has a note indicating whether they're async
	safe. An async safe function can be invoked in a signal handler
	or when the world is stopped by the GC. Conversely, a function
	that is not async safe must not be invoked in such a context or
	undefined behavior can occur (crashes, deadlocks, etc).

	<p>Some functions may only be invoked from a profiler module's
	init function (or prior to running managed code in the case of
	embedding). This is noted explicitly only if applicable to a
	function.

<h3>Basic Functions</h3>

	<p>These functions are used to load and install profilers.

<h4><a name="api:mono_profiler_load">mono_profiler_load</a></h4>
<h4><a name="api:mono_profiler_create">mono_profiler_create</a></h4>
<h4><a name="api:mono_profiler_set_cleanup_callback">mono_profiler_set_cleanup_callback</a></h4>

<h3>Code Coverage</h3>

	<p>These functions provide access to the JIT compiler's code
	coverage support. This functionality can be used to collect
	information about how many times certain code paths have been
	executed.

<h4><a name="api:mono_profiler_enable_coverage">mono_profiler_enable_coverage</a></h4>
<h4><a name="api:mono_profiler_set_coverage_filter_callback">mono_profiler_set_coverage_filter_callback</a></h4>
<h4><a name="api:mono_profiler_get_coverage_data">mono_profiler_get_coverage_data</a></h4>

<h3>Statistical Sampling</h3>

	<p>Statistical sampling can be used to interrupt managed threads
	based on a certain mode and frequency for the purpose of
	collecting data about their current work.

	<p>One common use case for this functionality, usually referred
	to as call sampling, is to collect a backtrace from every thread
	when a sampling hit event arrives. This data can then be compiled
	into a report indicating where a program spends most of its time.

<h4><a name="api:mono_profiler_enable_sampling">mono_profiler_enable_sampling</a></h4>
<h4><a name="api:mono_profiler_set_sample_mode">mono_profiler_set_sample_mode</a></h4>
<h4><a name="api:mono_profiler_get_sample_mode">mono_profiler_get_sample_mode</a></h4>

	<p>A callback must be registered to receive sample hit events.
	Please see the <i>Callback Registration</i> section below.

<h3>GC Allocations</h3>

	<p>Profilers can be notified about all GC allocations performed
	by a program or the Mono runtime.

<h4><a name="api:mono_profiler_enable_allocations">mono_profiler_enable_allocations</a></h4>

	<p>A callback must be registered to receive allocation events.
	Please see the <i>Callback Registration</i> section below.

<h3>Call Instrumentation</h3>

	<p>The JIT compiler supports instrumenting managed method entry
	and exit points so that a profiler callback will be invoked.

	<p>While such callbacks by themselves have traditionally only
	been useful for call count profiling and the like, Mono gives
	these callbacks access to the arguments, locals, and return
	value of instrumented methods (together referred to as the 'call
	context'). This enables many profiling scenarios that would
	otherwise have required explicit hooks in the base class
	libraries.

<h4><a name="api:mono_profiler_set_call_instrumentation_filter_callback">mono_profiler_set_call_instrumentation_filter_callback</a></h4>
<h4><a name="api:mono_profiler_enable_call_context_introspection">mono_profiler_enable_call_context_introspection</a></h4>
<h4><a name="api:mono_profiler_call_context_get_this">mono_profiler_call_context_get_this</a></h4>
<h4><a name="api:mono_profiler_call_context_get_argument">mono_profiler_call_context_get_argument</a></h4>
<h4><a name="api:mono_profiler_call_context_get_local">mono_profiler_call_context_get_local</a></h4>
<h4><a name="api:mono_profiler_call_context_get_result">mono_profiler_call_context_get_result</a></h4>
<h4><a name="api:mono_profiler_call_context_free_buffer">mono_profiler_call_context_free_buffer</a></h4>

	<p>Callbacks must be registered to receive method entry and exit
	events. Please see the <i>Callback Registration</i> section
	below.

<h3>Callback Registration</h3>

	<p>In addition to the above functions, there's a large set of
	functions for installing generic profiler event callbacks. These
	are generated from C macros and so are not documented here.
	Please refer to the <code>mono/metadata/profiler.h</code> and
	<code>mono/metadata/profiler-events.h</code> headers for a full
	listing of these.

	<p>Callback registration functions are all async safe and can be
	safely invoked from multiple threads at the same time, with the
	caveat that altering a registered callback from one thread will
	not immediately affect another thread that is already invoking
	the current callback.

<h2>API Stability</h2>

	<p>The profiler API does not have the same API stability
	garantees that the rest of the Mono embedding API does. While
	a breaking change to the profiler API is extremely rare, it has
	happened in the past when changing the API in a backwards
	compatible way was deemed to be too much work for too little
	gain.

	<p>Therefore, developers of profiler modules may rarely need to
	update their code to work with new versions of the profiler API.

	<p>Developers who wish to support older versions of the API can
	perform a compile time check of the
	<code>MONO_PROFILER_API_VERSION</code> macro and maintain code
	for both old and new versions.

	<p>To aid with transitioning to a new version of the profiler
	API, the Mono runtime will detect and reject loading profiler
	modules which were compiled against older profiler API versions.
